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José A. Franco, Juan A. Fernández, Sebastián Bañón and Alberto González

Six muskmelon (Cucumis melo L.) Galia-type cultivars (`Delada', `Gallicum', `Galor', `Melina', `Regal' and `Revigal') were tested for salt tolerance at the seedling stage and during growth in the field. Three levels of salinity (ECW 2.5 (control), 5.0 and 7.5 dS·m-1), established by adding NaCl to fresh water, were used. The effect of salinity on seedling growth was assessed by measuring the total leaf area 36 days after sowing. `Melina' was the most tolerant at this stage and during subsequent growth in field, with a relative seedling leaf area of 60 and a relative yield of 66 at 7.5 dS·m-1 salinity, both expressed as a percentage of the values obtained at the control level of salinity. `Delada' was the most sensitive to the highest level of salinity at both stages, with relative seedling leaf area and yield of 51 and 56, respectively. For all cultivars, a highly significant correlation (r = 0.99) was established between the influence of salinity on seedling leaf area reduction and on decrease in yield during field culture. The results indicate that the reduction in seedling leaf area can be a good selection criterion to facilitate rapid screening for salt tolerance in muskmelon.

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José A. Franco, Víctor Cros, Sebastián Bañón, Alberto González and José M. Abrisqueta

The influence of two irrigation treatments during nursery production on the post-transplant development of Lotus creticus subsp. cytisoides was studied. The treatments lasted 96 days and consisted of irrigating 2 days/week with a total of 2.3 L of water per plant over the whole nursery period (T-2) or irrigating six days per week with a total of 7 L of water per plant (T-6). T-2 plants had greater root length: shoot length ratio and higher percentage of brown roots, an indicator of more resistance to post-transplant stress. Minirhizotrons revealed more active root growth in the surface soil of the T-2 plants, although the plants of both treatments rapidly colonized the whole soil depth studied (0-160 cm deep). T-2 plants had greater stem length growth per unit of soil area covered.

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Arnoldo Michel-Rosales, Javier Farias-Larios, Juan Alberto Osuna-Castro, Elpidio Peña-Beltrán, Juan Manuel González-González and Héctor Javier Garibay-Bautista

At present, pitahaya (Hylocereus undatus Britt and Rose), a nonconventional crop and cactus native from Mexico, is considered very promising because of its high adaptability and tolerance to extreme agricultural conditions of tropical regions (poor soils, drought, and elevated temperatures), where they are cultivated. In addition, pitahaya fruit is well-accepted and identified as a nutraceutical food that lowers cholesterol and glucose levels in blood and might prevent stomach and colon cancers. However, little or no scientific information on chemical control alternatives of weeds in pitahaya commercial plantings have been generated. In this work, the phytotoxicity degree of seven commercial herbicides (metribuzin, glyphosate, glyphosate trimesium, paraqut, paraquat+diuron, atrazine, and halosulfuron methyl) in pitahaya plants grown under plant nursery conditions was assessed. A completely randomized design with 12 replications was used. The experimental unit was a flowerpot with a 5-month-old plants. The phytotoxicity degree was evaluated at 3, 7, 14, and 21 days after application using the scale proposed by EWRS. The herbicides that caused injury to the plants were paraqua+diuron (79%) and paraquat (77%), respectively. Metribuzin, halosulfuron-methyl, and atrazine did not cause any injury to the plants.

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Lucina Gómez-Pérez, Luis Alonso Valdez-Aguilar, Alberto Sandoval-Rangel, Adalberto Benavides-Mendoza, Rosalinda Mendoza-Villarreal and Ana María Castillo-González

Irrigation water high in alkalinity can severely compromise the growth and marketability of ornamental plants. In the present study we investigated the response of lisianthus to increased calcium (Ca) when irrigated with solutions containing high levels of bicarbonate (HCO3 )-induced alkalinity. Alkalinity in irrigation water reduced the growth of lisianthus; however, plants supplemented with an increased concentration of Ca at alkalinity levels from 4 to 7 meq·L−1 of HCO3 exhibited improved growth and dry mass (DM) accumulation or were not detrimentally affected, demonstrating that Ca contributes to the increase of the tolerance of lisianthus to alkalinity. Supplementary Ca did maintain a high stomatal conductance (g S) and transpiration rate when alkalinity was at 4 meq·L−1, which explained the lower water potential in young leaves. Plants irrigated with solutions containing supplementary Ca had higher total DM, which was associated with a higher g S; however, when conductance was higher than 0.280 cm·s−1, like in plants with no supplementary Ca, DM tended to decrease. At a typical Ca concentration, there was a disruption on stomata functioning as g S and transpiration rate increased, which was associated with a reduction in shoot potassium (K). Calcium ameliorated the uptake of K when alkalinity was 4 meq·L−1 by allowing a less marked reduction in shoot K concentration. Chlorophyll was reduced by increasing alkalinity as a result of a decrease in shoot iron (Fe); however, supplementary Ca also contributed in increasing plant tolerance to alkalinity at 4 meq·L−1 by sustaining a high shoot Fe concentration. Supplementary Ca increased catalase and peroxidase activities, indicating that lisianthus responded to the stress by enhancing the activity of these enzymes to reduce oxidative damage.